1. Field of Invention
This invention relates to an improved method for the assembly of lead-acid batteries and an apparatus related thereto. More specifically, the invention relates to a flexible, high speed method for the manufacture of lead-acid batteries in a wide variety of sizes and configurations from continuous lengths of battery plate stock.
2. Description of the Prior Art
Conventional lead-acid storage batteries generally consist of a plurality of alternating flat pasted positive plates and flat pasted negative plates which are electrically insulated from one another by a porous separator material. The cell assembly so constituted is placed into a suitable container in which the positive and negative plates are brought into contact with a sulfuric acid electrolyte. In batteries containing free electrolyte, the cell assembly is generally fully immersed in the sulfuric acid. In batteries containing no free electrolyte, the sulfuric acid is fully absorbed in the plates and separator material.
The manufacture of storage batteries of the type described hereinabove, generally involves alternately stacking cured pasted positive plates and cured pasted negative plates to form a cell assembly in which each positive plate is separated from each negative plate by a porous separator material. The cell components are aligned such that all of the positive current collecting lugs are aligned with one another. All of the negative current collecting lugs are aligned with one another in a zone significantly separated from the plane of the aligned positive lugs. The porous separator material overlaps the plates on four sides to provide effective electrical insulation. The positive lugs are electrically connected to one another and the negative lugs are electrically connected to one another by means of separate electrically conductive plate straps. The completed cell assembly is placed in a battery container. If the battery contains more than one cell, intercell electrical connections are then made and the battery container and cover are sealed together. The sulfuric acid electrolyte is next added to the battery and the plates are electrochemically formed. Following electrochemical formation, the acid used for formation may be removed from the battery and replaced with sufuric acid of a different specific gravity. The battery is then washed and dried, vent caps are installed, and the final production steps are completed.
An alternative method of manufacture involves the use of individual positive and negative plates that have been electrochemically formed, washed and dried prior to cell assembly. This method eliminates the need to electrochemically form the plates in the battery container, thereby increasing the speed and minimizing the cost of final assembly. These cost savings are generally offset, however, by the added cost of additional handling of the very large number of individual plates involved prior to the cell assembly operation.
Generally, pasted battery plates are cured and, if electrochemically formed prior to assembly, formed as "doubles", i.e., two attached plates which must be separated prior to the cell assembly step. One method of separating paired battery plates which is disclosed in U.S. Pat. No. 4,285,257, involves a rotary cutting blade which separates a stack of paired plates into two stacks of individual plates of the same polarity which represent the starting material for commonly used cell assembly processes, such as those described in U.S. Pat. Nos. 4,784,380, 4,720,227, 4,728,093, 4,534,549, 4,168,772, and 3,982,624. All of these methods and related apparatus utilize feedstock consisting of stacks of singular negative plates, stacks of singular porous separator pieces, and stacks of singular positive plates which are automatically combined on a conveyor to progressively form cell assemblies containing the desired number of positive plates, negative plates, and separator pieces which normally overlap the positive and negative plates on four sides. The battery cell assemblies so produced must be removed from the conveyor and the positive and negative plate lugs aligned in a separate operation prior to the subsequent production steps of forming the positive and negative plate straps and inserting the completed cell assembly into the battery container.
U.S. Pat. Nos. 4,479,300, 4,510,682, and 4,583,286 describe alternative methods and apparatus for the production of a lead-acid battery cell assembly which involve building a cell assembly from a plurality of positive plates obtained from a source of individual positive plates, a plurality of negative plates obtained from a source of individual negative plates, and a continuous length of porous separator material containing accordion-type folds. In this construction, the positive and negative plates are located within accordion folds and are on opposite sides of the separator from one another. The cell assemblies so produced are subjected to additional production steps in which the positive plate lugs and negative plate lugs are properly aligned, the cell assembly is taped together to hold the alignment during the subsequent and separate production steps of forming the plate strap and inserting the taped cell assembly into the battery container.
Another known method for the production of lead-acid battery cell assemblies from stacks of singular positive plates, stacks of singular negative plates, and a continuous length of porous separator material involves properly locating a positive plate on top of a piece of separator material cut from said continuous length such that the length of the cut piece is at least twice the height of said positive plate, folding the separator material over the bottom of said positive plate and sealing it on both sides to form a 3-sided envelope, properly positioning said negative plate relative to the envelope containing the positive plate, and repeating these steps until the cell assembly contains the desired number of positive and negative plates. A rotary apparatus utilized in this production method, described in U.S. Pat. No. 4,822,834, removes the aforesaid battery plates from the stacks of individual plates of singular polarity and positions the plates relative to the separator and each other.
Cell assemblies produced in accordance with the above method and apparatus must be physically removed from the apparatus and subjected to separate production steps in which the positive and negative plate lugs are aligned, the plate straps are formed, and the cell assembly is inserted into the battery container. U.S. Pat. No. 4,824,307 describes a method and apparatus for automatically transporting and aligning said cell assemblies prior to subjecting them to a means for forming the positive and negative plate straps.
All of the hereinbefore described methods and apparatus involve extensive and costly handling of paired and singular plates prior to cell assembly and each requires additional production steps to align the plate lugs and insert the cell assembly into the battery container. Further, each requires a significant expenditure in dust control equipment in order to comply with mandated lead-in-air standards when as-cured plates are being handled.
A method and apparatus for the production of lead-acid battery cell assemblies from continuous lengths of cured battery plate stock and continuous lengths of separator material, is disclosed in U.S. Pat. No. 4,982,482. In this method, the required lengths of a plurality of cell components: e.g. a length of cured positive plate stock, a length of porous separator material, a length of cured negative plate stock, and a second length of porous separator material, all of which represent only a portion of the total number of cell components in the completed cell assembly, are indexed into a cutting chamber and simultaneously cut to length by a single cutting mechanism. The subassembly so produced is next transported to a stationary accumulation chamber where it is stored to await the cutting and transport of the remaining portions of said cell assembly. The process is then repeated until all of said portions are in the stationary accumulator chamber after which the components are moved as a unit into an alignment chamber in which the positive and negative plate lugs are aligned and the desired degree of separator overlap relative to each plate is achieved. The final cell assembly also contains two rigid end-plates, each containing outwardly projecting "wings", which are taped tightly circumferentially in a separate step and which, together with the plate and separator assembly, make up a rigid self-contained unitized cell module which can be easily handled during subsequent manufacturing steps which include insertion of the cell assembly into the battery container, formation of the positive and negative plate straps, formation of intercell connectors, sealing of the top cover to the cell container, addition of electrolyte, and electrochemical formation of the plates in the container. Upon completion of formation, the battery is washed and dried and final assembly is completed.
Although the above method eliminates the heretofore described economic and ecological problems inherent in the cutting and handling of singular and paired battery plates, it still requires that a plurality of cell sub-assemblies be fabricated and transported to, and accumulated in, a stationary chamber; the final cell assembly be realigned after all sub-assemblies have been accumulated; separate rigid winged end-plates provide cell compression and hold the cell firmly in the container, and that the cell assembly be rigidized by taping in order to facilitate handling during transport to, and insertion of the completed cell assembly into, the battery container. Further, the need to electrochemically form the cured plates in the battery container prior to final assembly interrupts the smooth flow of the subsequent assembly steps and increases the cost of manufacture.
None of these prior art cell assembly methods are adapted to achieving the required alignment of the cell components during the cell assembly operation, building a cell stack and inserting the stack into the battery container in a single continuous operation, and continuous "downstream" assembly operations that are uninterrupted by the need to electrochemically form the plates after insertion of the cell assembly into the battery container. There remains, therefore, a need for a practical method of properly aligning the positive and negative plate lugs during the cell assembly process, placing the completed cell stack directly into the battery container as the last step in the cell assembly process, and eliminating the need to electrochemically form the plates in the battery container. A process incorporating these improvements would substantially reduce the cost of producing lead-acid batteries and greatly improve worker safety.